1. Field of the Invention
This invention relates to the field of radiography, and more particularly to apparatus for providing real-time radiographic monitoring of breast tissue during a stereotactic needle biopsy procedure.
2. Description of Related Art
X-ray mammography is a diagnostic procedure in which the breast of a patient is X-rayed and the resulting X-ray film is inspected to determine whether there are any microcalcifications or other growths or lesions in the breast tissue. If a lesion or growth is visible in the X-ray film, then it is often necessary to perform a biopsy procedure to determine if the lesion or growth is benign or if it requires immediate treatment. Although the X-ray film can be used to give a rough estimate of the position of the lesion, breast tissue is highly malleable and thus new images of the breast must be taken immediately before the biopsy procedure is performed, and after the breast has been compressed and clamped. In order to precisely locate the biopsy needle relative to the lesion, conventional equipment requires that multiple images be taken, which in turn necessitates repositioning and reclamping of the breast. Such procedures are time-consuming and uncomfortable for the patient.
Recently, systems have been developed which allow the breast to be clamped once, and the X-ray source moved to different positions and monitored on a video screen during the biopsy procedure in order to provide real time guidance of the biopsy needle without the need to reposition the breast each time a new image is taken. The present invention is designed to be used with systems of the general type disclosed in U.S. Pat. No. 4,821,727, and in particular with apparatus designed by Bennett Corporation and illustrated in FIG. 1 (which also shows a portion of the preferred invention).
In the Bennett system, and others of its type (including the one disclosed in U.S. Pat. No. 4,821,727), the patient to be examined is seated in a chair 10 which is adjustable so that the patient can be comfortably positioned with the breast to be examined being located on a table 24. An X-ray source 16 is mounted on a pivotal arm 18 so that the target area can be exposed to X-rays at different angles in order to form a stereoscopic image of the breast without having to unclamp and reposition the breast each time a new image is taken. However, in the Bennett system, instead of using two relatively movable plates to compress the breast, as disclosed in U.S. Pat. No. 4,821,727, a single movable plate 22 serves to compress the breast against a table top in order to keep it stationary and provide for a uniform X-ray exposure.
In the Bennett system, as in other similar systems, images captured by the X-ray camera device, to be described in detail below, are displayed on a monitor 28, and used by the physician to guide a biopsy needle 20 to a targeted tissue within the breast by means of an electronic controlled biopsy needle actuator and appropriate cursor controls for enabling azimuth, elevation, and depth of insertion adjustments to be made. Conventionally, an image of the needle is included in the image of the breast, and a variety of means are known for providing reference points in the display to assist in guiding of the biopsy needle to its target.
The present invention is an imaging system suitable for use with the Bennett apparatus illustrated in FIG. 1. However, it will be appreciated by those skilled in the art that the principles of the invention may be used with apparatus other than the Bennett apparatus specifically disclosed herein. These principles involve improvements in the x-ray camera used to capture the image and in the image processing circuitry which offer a number of advantages over imaging systems used in prior apparatus, including the imaging system disclosed in U.S. Pat. No. 4,821,727, cited above. In the system disclosed in U.S. Pat. No. 4,821,727, for example, the X-rays are first caused to strike a fluorescent screen, with the resulting visible light image being captured by a lens and video camera system. In order to provide a usable display, this prior imaging arrangement requires an "image intensifier" coupled to the fluorescent screen output via a mirror or prism and/or fiber optics (see col. 5, lines 50-65 of U.S. Pat. No. 4,821,727). Such an imaging system is both structurally complicated and lacks the error correction capabilities and other processing advantages of a digital system.
In U.S. Pat. No. 5,289,520, an X-ray mammography system is disclosed which utilizes a more sophisticated digital imaging system but less than optimal optics. In this type of system, the X-rays are captured by a phosphorescent plate, which in turn emits photons at visible light frequencies. The photons emitted by the phosphorescent plate are focused by a lens system onto a CCD array, and the output of the CCDs are applied through a preamplifier, transmitted over an analog bus, and subsequently digitized for further processing. While use of digital image enhancement software provides magnification, contrast enhancement, window level manipulation and high resolution images, with low exposure levels, short exposure times, and greatly reduced imaging time, and thus represents an improvement over the system disclosed in U.S. Pat. No. 4,821,727, digital systems of the type disclosed in U.S. Pat. No. 5,289,520 nevertheless have the disadvantage of being relatively complex, with little attention given to patient comfort (in the system disclosed in U.S. Pat. No. 5,289,520, for example, the patient must assume a relatively uncomfortable prone position for the duration of the imaging procedure, as opposed to the seated position shown in FIG. 1.